The present invention pertains to features and methods that protect components of a clamshell apparatus during electroplating, electropolishing, electroless plating or other wet deposition process.
U.S. patent application Ser. No. 10/010,954, filed Nov. 30, 2001, by Patton et al. (incorporated herein by reference) describes an exemplary “clamshell” apparatus for electrochemically treating semiconductor wafers. As described there, a “cup” and “cone” of a clamshell apparatus can take many forms. In one embodiment, the cup of has a ring structure with a flat top surface (including an inner circumferential edge or “lip” as shown in FIGS. 1F–I of U.S. patent application Ser. No. 10/010,954). Generally, the cup and cone assembly holds, positions, and rotates a wafer during, for example, electroplating, electroless plating, electropolishing, or other wet chemical deposition or removal process. A lipseal on the lip of the cup may contain embedded contacts for delivering plating current to a seed layer on a wafer. The clamshell provides backside protection to the wafer. In other words, electrolyte is prevented from contacting the edge and backside wafer when immersed during a plating process. Backside protection is afforded by fluid-resistant seals that are formed when the cup and cone engage one another to hold a wafer (refer to U.S. patent application Ser. No. 10/010,954 for more description).
Plating solution is generally comprised of a solution of metal ions in acidic or basic aqueous media. For example, an electrolyte may be composed of copper sulfate dissolved in dilute sulfuric acid. During processing, plating solution is often splashed into parts not wetted during immersion; for example the cone, rotation components, seals, vacuum sealing components, and the like. Solution in these areas evaporates, causing copper sulfate to precipitate out of solution and crystallize. These crystals cause particle contamination, metallic contamination, and mechanical reliability problems when they deposit on mating surfaces.
In a somewhat related issue, electrical contacts, which deliver plating or polishing current to the wafer, can become contaminated and their performance degraded after thousands of cycles. Also, reverse pulse plating has been found to lead to copper build-up on the lip seal. Further, reversible failure can occur even when the plating system sits idle. It is therefore desirable to have rinsing and drying capability of the contact and lip seal area to prevent contamination build-up, thereby improving tool and process reliability.
Sealed contacts necessarily have a high profile step at the edge of the lip seal which creates a “pocket” where liquid remains even when rotated at high rotational speeds. Furthermore, the step creates a stagnant zone, trapping rinsate and preventing thorough rinsing of the wafer surface.
To address these problems arising from plating solution contacting sensitive clamshell components, improved designs are required.